Time-dependent behavior of posttensioned concrete pavements under environmental loading

The performance of cast-in-place posttensioned concrete pavement (PTCP) constructed in 1985 on I-35 in Waco, Texas, has been excellent. Encouraged by the performance of the section, the Texas Department of Transportation began construction of another PTCP project in 2008 on I-35 in Hillsboro. In this study, the time-dependent behavior of PTCP under environmental loading was experimentally investigated and its implications in PTCP design investigated. Concrete strain and slab movement as well as temperature and relative humidity were measured. The effects of such factors as posttensioning (PT) force, friction, curling stress, creep, and shrinkage on the behavior of PTCP were investigated. The stress introduced by longitudinal PT varied along the slab length, with a maximum near the armor joint and a minimum at the center of the slab. The variations were induced by the friction between concrete and subbase. The concrete strain at middepth of the slab under environmental loading was also affected by friction. The concrete thermal strain restrained by friction was larger near the slab center, and the degree of restraint was 20%. The distribution of longitudinal slab movement was nonlinear along with the distance from the slab center, and 13% of free slab movement was restrained at the armor joint. Continued contraction of the concrete slab due to creep and shrinkage was observed, which will result in the opening of joint width. Because creep and shrinkage are long-term effects, slab movement monitoring will continue until their effects become insignificant and the information gained should be used for the design of initial joint width.